Binocular visual mechanisms relevant to the perception of the positions and movements of objects in three-dimensional space will be studied by the method of single-unit analysis in the cerebral cortex of visually active, alert monkeys. Stimuli will be presented stereoscopically using a dual-screen, computer-controlled, electronic display system. The position of both eyes will be monitored continuously in order to evaluate the extent of behavioral control of the monkey's oculomotor activity. The sensitivity of each neuron to position in depth will be tested with stationary moving stimuli presented at various apparent depths. The possible role of these neurons in global and dynamic stereopsis will be tested by analysing responses to random-dot stereograms and to stimuli that appear to move toward or away from the monkey in different directions and at different speeds. The objective of this research is to identify populations of neurons whose activity is related to specific aspects of stereoscopic vision, to interpret the significance of these populations by comparing our physiological findings with psychophysically determined capacities for depth perception in man and monkey, and to reconstruct the anatomical distribution of the neurons studied as a means of understanding the functional organization of the visual cortex that makes possible normal binocular vision.